Polarized epithelial cell migration depends on rear end stress fiber tension
|Titel||Polarized epithelial cell migration depends on rear end stress fiber tension|
|Ort||MMCM2018 - International Symposium Measuring and Modelling Cell Migration, Vienna, Austria, September 27-25, 2018.|
Actin stress fibers (SFs) play a central role in cell adhesion and migration. Recently laser ablation has become a popular tool to understand mechanical properties of actin SFs and to measure forces generated by a single or multiple actin SFs in non-locomoting or patterned cells, but still less is known about the role of individual actin SFs in migrating cells. In this study laser nanosurgery combined with live-cell microscopy was applied to understand several aspects of actin SFs contribution cytoskeletal organization. First, the input of the actin ventral SF at the rear end of the polarized cell to cell polarity and migration in human keratinocytes (NHEK) was analyzed. The second part was devoted to investigation of a contribution of the SFs of different localizations in cell, namely, SFs in lamellae, in support of cell polarity and locomotion. And finally, mutant murine keratinless keratinocytes were used as a convenient cell model to better understand participation of intermediate keratin filaments in cell polarity.
We showed that severing of the actomyosin rear end SF results in subsequent disassembly of the composing it proteins from the ablated ends: myosin II, α-actinin and zyxin which reflect loss of tension in the ends of the cut SF. The loss of tension was followed by generation of a new actin fiber at the sire of ablation. Formation of the new actin fiber included incorporation of these molecules but was insufficient to maintain the rear end, and at the site of ablation a cell membrane started protruding in a mode of lamellipodium, finally leading to global cell shape reorganization, pancake-like cell shape and temporal stop of migration.
Laser destruction of the ventral SFs in lamellae demonstrated the importance of a structural integrity of this SFs for a preserved cell polarity and migration. The cells demonstrated the following behavior upon the laser ablation: formation of the membrane protrusion at the rear end, loss of polarity, acquisition of a circle-like shape accompanied by the vanishing of ventral SFs, generation of transverse arcs and dorsal SFs and halt of migration.
Keratin filaments in its turn were shown not to possess an inevitable role in cell polarity and migration – in both types of the local laser ablation experiments, laser cuts of the rear end SFs and ablation through all the SFs in lamellae, the keratiness keratinocytes demonstrated cognate reorganization of the cell shape as in the experiments with the nHEKs expressing keratins, briefly, formation of the membrane protrusion at the rear end and loss of polarization.
Thus, laser nanosurgery proved to be a useful tool in understanding of the local importance of the cytoskeletal structures and, in particular, that myosin-derived tensile SF at the rear end of the polarized migrating cells as well as the structurally integral SFs in lamellae are of great importance for cell polarity and migration.